Ice cores reveal two major solar storms in the last 1300 years

Ars Technica : Spikes of carbon-14 in tree rings dating to 774–75 CE and 993–94 CE have been linked to the presence of radioactive beryllium in polar ice cores. According to Raimund Muscheler of Lund University in Sweden and his colleagues, who found the beryllium, their discovery suggests that major solar storms, rather than more exotic events such as a giant comet hitting the Sun or a nearby supernova, were the source of both isotopes. Muscheler’s analysis of the solar storms suggests that they were both more powerful than the strongest recorded solar storm to have hit Earth—the 1859 Carrington event , named for the British astronomer who discovered and tracked the flares. It is estimated that if a storm similar to the Carrington event were to hit Earth today, the resulting power outages could last for at least five months and disrupt almost all communications satellites.